Animal fat, which is present in much animal feed, significantly limits the shelf life of such feed. Antioxidants have been found to improve the stability and to add to the shelf life of animal-fat-containing feed. Although there is a pressing call for animal feed without synthetic antioxidants, the cost of natural antioxidants (in the amount considered to be required) has heretofore been prohibitive.
In excess of 95 percent of the animal (mammal and/or poultry) fat used in animal feed (including pet food) is what is referred to as inedible (not for human consumption) fat, which differs significantly in antioxidant requirements from such animal fats as lard, which is edible fat. Due to the nature of raw materials from which it is derived, inedible fat often contains substances, e.g. trace metals, which serve to catalyze oxidation. For this reason, antioxidant systems intended for use in inedible fats have historically contained chelators, such as citric acid, to inactivate such substances.
Lecithin was reported as a "synergist" for antioxidants, such as tocopherol, in animal feed supplements in U.S. Pat. No. 3,293,131. The presence of fat and lecithin in pet food matrix forms is referred to in U.S. Pat. No. 3,908,025. U.S. Pat. No. 4,450,097 is directed to an antioxidant (suitable for adding to foodstuffs) extracted from rosemary. A synergistic effect was found (U.S. Pat. No. 4,525,306) for an antioxidant component (used to prevent oxidation of fats) extracted from sage and rosemary, commercial soybean lecithin and ethyl alcohol.
According to Hudson and Ghavami [Lebensm.-Wiss. U. Technol, 17:191 (1984)] "Certain phospholipids have been shown to exert synergistic effects with the primary antioxidant tocopherols in inhibiting autooxidation of polyunsaturated fatty acids in model systems based on both lard and soybean oil."
Oil of rosemary is an antioxidant which helps to stabilize fats according to Kalsec.RTM.'s technical data sheet (Publication No. R-10, June 1988) for Herbalox.RTM. seasoning. Enzyme-modified lecithin has been designed to enhance both water dispersibility and oil-inwater emulsifying properties of feed grade fats according to Central Soya's specifications for Blendmax.RTM.. Papas (PETFOOD INDUSTRY, 8 to 16, May/June 1991] report on antioxidants for pet food products; in addition to tocopherols, which are effective antioxidants for, e.g., lard, lecithin is regarded as a weak antioxidant. Han (JAOCS, Vol. 68, No. 10, 740 to 743, October 1991) reports antioxidative effects of tocopherol on the oxidation of sardine oil and indicates that "Lecithin can act as an antioxidant in inhibiting autoxidation of polyunsaturated fatty acids. In discussing "Synergistic Antioxidative Effects of Tocopherol and Ascorbic Acid in Fish Oil/Lecithin/Water System" (JOACS, Vol. 68, No. 11, 881 to 883, November 1991), Yi states:
Because lecithin acted not only as a primary antioxidant but also as a synergist to tocopherol (9), its presence for solubilizing ascorbic acid makes it difficult to interpret the synergistic property of ascorbic acid and .delta.-tocopherol. PA1 a) from 0.01 to 2.0 (preferably from 0.01 to 0.10) parts by weight of lecithin, PA1 b) from 0.0035 to 0.2 (preferably from 0.0035 to 0.056) part by weight of tocopherol, and PA1 c) from 0.01 to 0.20 (preferably from 0.01 to 0.10) part by weight of oil of rosemary.
In addition, natural mixed tocopherols are sold by Eastman as foodgrade antioxidants.